(i) Field of the Invention
This invention relates to a process for the production of a block copolymer of propylene, and specifically to a process for the production of a propylene block copolymer of uniform quality by the combination of a particular polymerization process and a specific control method.
(ii) Description of the Prior Art
Many processes have already been well-known and proposed to produce block copolymers of propylene in order to improve the impact resistance of polypropylene, especially, its low-temperature impact resistance (see, for example, Japanese Patent Publication No. 20621/1969, Japanese Patent Publication No. 24593/1974, etc.).
In the meantime, as polymerization processes permitting multi-stage copolymerization of ethylene and propylene at different reacted ethylene/propylene weight ratios in relatively fewer polymerization tanks, the present inventors have also proposed to produce block copolymers by combining a continuous polymerization process and a batchwise polymerization process (see, for example, Japanese Patent Laid-Open No. 145114/1982, Japanese Patent Laid-Open No. 145115/1982, Japanese Patent Laid-Open No. 149319/1982, Japanese Patent Laid-Open No. 149320/1982, etc.).
The above-described processes featuring the use of a continuous polymerization process and a batchwise copolymerization process in combination are excellent processes which allow to produce block copolymers of various quality in a polymerization apparatus comprising fewer polymerization tanks connected together. They are however accompanied by a problem that fine quality control is difficult, because the amount of a slurry to be charged into each batch reaction tank and the concentration of the slurry do not remain constant due to differences in performance between catalysts of different lots, variations in quality of raw materials and/or the like in actual production on an industrial scale even when the polymerization apparatus is operated under constant conditions.